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Kingdom Protista – Characteristics, Classification, Importance, Examples

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  • Last Updated : 31 Jul, 2022
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In biology, we learn that even the smallest and most insignificant creatures have vital responsibilities to play when it comes to maintaining living beings. This is something that we come to realize as we study biology. In spite of their microscopic size and limited capabilities, the Protista are one of the groups of organisms that contribute significantly to the process of cell organisation. Ernst Haeckel, a naturalist of German descent, was the one who first introduced the idea of the kingdom Protista in the year 1866.

Protists are distinguished from other organisms in a number of ways, the most notable of which is the fact that their cell distribution is ordered, in addition to the fact that they have nuclei and organelles. It is possible that members of the kingdom Protista should be referred to as “aquatic creatures.” Since protists belong to the eukaryotic kingdom, they contain components enclosed in membranes and a nucleus clearly demarcated from the rest of the cell.



Protista: Some History and Background Information

In 1969,Robert Whittaker presented his categorisation of the world’s 5 kingdoms, and the kingdom of the Protista was one of those five kingdoms. At that time, protists were thought of as unicellular eukaryotic creatures despite their multicellular structure. However, as time progressed, the kingdom Protista grew, and it eventually became home to even multicellular species.
The creatures that are designated as belonging to this kingdom are distinguished by the fact that each and every one of those species has a simple cellular structure that is devoid of any superfluous tissues or organs. So far, scientists think that more than two lakh different types of protists have indeed been found. In point of fact, in addition to the enormous number of protists that have previously been found, there are still an extremely large number of protists that have not been found. Because protists are creatures that live in water, the majority of their habitat is comprised of aquatic environments. They are the most important producers in the ecosystem, which means they help to construct its fundamental structure. In addition to this, protists exist in a wide variety of sizes, ranging from very small creatures to enormous seaweeds that are capable of reaching heights of roughly 61 metres (about 200 ft). Protista traits and characteristics Because Protista is such a diverse kingdom, it is challenging to simplify its characteristics in a way that is consistent and captures their uniqueness. In terms of their morphology, reproductive capabilities, and dietary requirements, the creatures that belong to this kingdom exhibit a wide range of variety and complexity.

On the other hand, we may summarise the qualities that Protista has in the following manner

Some organisms may consist of just a single cell, while others may include colonial or multicellular structures.
The organisational structure of protists may vary greatly due to the fact that they belong to the kingdom of eukaryotic organisms. Protists, for example, include many organelles, such as a nucleus, mitochondria, plastids, feeding vacuoles, and flagella. 

  • One of the qualities that distinguish protista from other types of organisms is their capacity for both sexual and asexual reproduction.
  • Protists are organisms that can live on their own, but they can also live in symbiotic relationships with those other organisms.
  • The interaction that takes place between a protist and another organism may either take the form of mutually beneficial cooperation or harmful parasitism. 
  • In a connection that is not parasitic, the protist derives the advantage by feeding off the host. This is in contrast to a relationship that is parasitic, in which the protist derives the benefit by working together with the host. In most cases, protists provide humans with a choice between two distinct outcomes: one outcome is advantageous to human health, while the other outcome is detrimental to human health in the form of potentially fatal illnesses. 
  • Protists have the dual properties of both movement and immobility, making them an essential element of the plankton aquatic system. Protists are now at the bottom of the food chain, but they’re an important part of marine life. Some types of protists are able to move about by walking on their cilia, flagella, or pseudopodia; however, other types of protists are sedentary and don’t move at all.
  • One other quality of protists is that they are capable of both autotrophy, or the process of producing their own food, and heterotrophy, or the process of obtaining their nourishment from sources other than themselves. Holotropic nutrition involves the organism seizing and ingesting the food, while saprotrophic nutrition involves the microbe releasing enzymes that transform organic compounds into simpler products. 

Classification of the Kingdom of Protista

The kingdom of Protista is composed of three different kinds of organisms: those that resemble plants, those that resemble fungi, and those that resemble animals. Plant-like Protists These are creatures that exhibit traits similar to those of plants and are also species capable of photosynthesis. Dinoflagellates, chrysophytes, and euglenoids are the three subtypes that fall under this category.


The class Dinophyceae is comprised of around one thousand different species of photosynthetic protists and is classified under the division Pyrrophyta.

  • They get their sustenance through photosynthesis, often known as the autotrophic process.
  • These are forms that move, and have two flagella, but are primarily found in the ocean.
  • They have pigments of different colours, such as green, yellow, brown, red, or blue.
  • These make up some of the most essential parts of phytoplankton.
  • Their macronuclei have compacted chromosomes, even when they are in the interphase phase; this is referred to as mesokaryon.
  • Certain types of dinoflagellates give forth light and may be seen glowing in the dark. This is a reference to the natural process known as bioluminescence.
  • In addition to this, they expel poisons into the environment, which not only give the water a reddish colour but also harm marine life. The colouration of the dinoflagellates is another factor that contributes to this red tide, and this phenomenon of red tide is seen when the organism is rapidly reproducing.
  • There is the potential for sexual as well as asexual reproduction.
  • Examples: Gonyaulax, Noctiluca, etc.


These are sometimes referred to as the gems of the plant kingdom

  • These are free-floating, unicellular forms of fresh or salt water that may be found wherever.
  • The majority of them are photosynthetic, and the silica and pectin that make up their cell walls are what give their cells their structure.
  • Reproduction may occur either sexually or asexually, depending on the circumstances.
  • The term “diatomaceous earth” refers to the material that results from the aggregation of a significant number of diatoms’ cell wall deposits (which can be used as fuel after mining).
  • The cell walls of diatoms are formed by two thin shells that cover one another and fit together like the lid and base of a soapbox.
  • Example: Diatoms, Desmids, golden algae, etc


These are unicellular and have features with both plants and animals, albeit they behave more like animals. 

  • They are green and get their sustenance from autotrophic sources (plant character).
  • These are unicellular flagellates (animal characters) that are similar to Euglena and are most often seen in still freshwater.
  • They have two different forms of flagella, one called Long Whiplash and the other called Short Tinsel.
  • Instead of having a cell wall, they have something called a pellicle, which is a protein-rich layer that allows their body to be flexible.
  • The meal is kept in granules that are made of protein and are known as pyrenoids.
  • Only the asexual method can be used to make more of the same kind.
  • In the dark, photosynthetic euglenoids change their feeding behaviour to that of heterotrophs; this kind of diet is referred to as mixotrophic.
  • Take the genus Euglena as an example; it is the most important member of this group and is considered to represent the transitional link between plants and animals.

Fungi-Like Protists (Slime Moulds)

As a result of the fact that they have features with both animals and fungi, we collectively refer to them as fungus-animals. 

  • You may find them in damp terrestrial settings, and you can watch them move over the rotting twigs and leaves.
  • They are capable of reproduction via both sexual and asexual means.
  • These demonstrate the presence of saprophytic nourishment.
  • Plasmodium may be produced by them under the right circumstances. These are split into 2 groups based on whether or not they have the parasite Plasmodium: a. Slime moulds with no cells or Plasmodium, such as Fuligo septica, Physarum, etc. cellular slime moulds such as Dictyostelium, Polysphondylium, and other similar organisms.

Animal-Like Protists (Protozoans) 

These protists, also known as protozoans, are creatures that engage in heterotrophic metabolism. They are the animals’ most distant ancestors. They may be broken down into four primary categories, which are as follows:

Amoeboid protozoans

  • They may be found in saltwater, as well as freshwater, and wet soil.
  • Similar to amoebas, they move with the assistance of a set of pseudopodia.
  • Other members of this group include Entamoeba histolytica and E. gingivalis, both of which, when swallowed after being exposed to polluted water, may result in a variety of digestive and mouth disorders or infections.

Protists that have flagella

  • In the wild, they either live on their own or are parasites.
  • Few are the most important organisms in this group:
    • Trypanosoma species can spread some dangerous diseases. The tsetse fly is the one that spreads them. 
    • Sand flies are the vectors for the Leishmania species that are responsible for kala-azar and dum-dum fever.
    • Giardia sp. – causes giardiasis.
    • Leukorrhea is caused by the bacteria Trichomonas vaginalis.

 Protozoa that have cilia

  • These organisms live in water and move about thanks to the presence of cilia on their bodies.
  • They exhibit nuclear dimorphism, having both macro and micronuclei, as in the case of Paramecium and other similar organisms.
    • The vegetative nucleus, also known as the macronucleus, plays a role in the regulation of metabolic processes and growth.
    • Micronucleus, also known as the reproductive nucleus, is an important component in managing reproduction.


  • In their life cycle, these Sporozoans go through a stage that is similar to a spore and is contagious.
  • All are endoparasites.
  • These organisms move with the assistance of organelles known as cilia, flagella, and pseudopodia, which are locomotory structures.
  • Example: Plasmodium, Monocystis, etc.

Economic Importance

The following is a list of the economic significance of Protista:

  • Protists are highly essential links in the food chain that exists in aquatic environments.\
  • In various regions of the world, some varieties of seaweed are used in the culinary process.
  • Diatomaceous earth can be used as a fuel source after it has been mined (Most of the oils and gasoline supply comes from diatoms fossil beds).
  • Some of the protists have the potential to be used in the manufacturing of various pharmaceuticals, vitamins, and cosmetics.
  • Storage components from the sheets of these diatoms are utilised in a variety of products, including toothpaste, paint, cleaners, and automobile polishes.
  • Red algae are a source of preservatives, an algin that is used in the manufacture of a variety of foods, including chocolates, ice creams, cereals, sweets, marshmallows, jams and jellies, and other confections

Conceptual Questions 

Question 1: Describe the protists? 


Protists are a large group of organisms with a nucleus that can be single-celled or have many cells. They also have parts of their cells called organelles that are very specialised and help them do different things. Most protists are free-living autotrophs, like algae, but some, like an amoeba, eat other things or are even parasites (Trypanosoma protozoa)

Question 2: What kind of living thing is Protista?


Protists are normally eukaryotes which are neither plants, animals, nor fungi. Protists have only one cell, but they can also live in groups of cells. Most of them are living in moist places on land, or even as parasites on other organisms.

Question 3: List the things that makeup Kingdom Protista?


Eukaryotic cells make up all protists. This means that their nucleus and other cell organelles are enclosed by a membrane.  Just about all protists lead life in water, a few  of them will be  live in  wet and moist places. Most protists are single-celled, but some, like the giant kelp, have more than one cell. They can be autotrophic or heterotrophic, and some even feed on other organisms.

Question 4: Have all Protists unicellular?


No, some Protists are multicellular. Molds and algae are both examples of protists that are made up of more than one cell. The kingdom Protista is made up of single-celled organisms like an amoeba, paramecium, and euglena.

Question 5: How does Kingdom Protista move?


Protists can move in three ways: with pseudopodia(false feet), flagella, or cilia. Many protists have flagella or cilia that they knock or sweep to move around in water.

Question 6: How do they get their energy?


They get their energy from the sun. Many other living things get food from their cells. These protozoa also make oxygen, which is good for many other living things. Both of these functions are similar to what plants do.

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